exact colour correction?

Discussion in 'Photoshop Tutorials' started by Peter, Oct 23, 2005.

  1. Peter

    Peter Guest

    I'm working some shots and I've always eyeballed my color correction using
    levels in RGB on a channel by channel basis. I tighten the highlights and
    shadow arrows to the histogram also with a final tweak on the mid tones in
    rgb. I use the alt key and stop when I'm going to lose info on highlights or
    shadows. I don't know if its me but is there a better and more exact way of
    doing this? I seem to have on occasion a miniscule but bothersome color cast
    on close inspection, it passes to the layman but for me I really need this
    to work. Consistency here is very important.

    Any input please.

    Peter, Oct 23, 2005
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  2. Peter

    Mike Russell Guest

    Hi Peter,

    Your procedure is a good start. Relying on the histogram in the way you
    describe improves contrast, but will introduce color casts in quite a number
    of images.

    One approach that addresses this issue is the shadow, highlight, and neutral
    drill, outlined in Dan Margulis's books. If you have Windows Photoshop, and
    are interested in learning how to do this, consider taking the Curvemeister
    class, which is free and starts on the first Sunday of each month.

    Many people use the Curvemeister demo for the class, and most of the
    techniques that I teach in the class may easily be carried over to Photoshop
    Mike Russell, Oct 23, 2005
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  3. Peter

    Bob Williams Guest

    When you say "I seem to have on occasion a minuscule, but bothersome,
    color cast on close inspection", do you mean the PRINT has the cast or
    your MONITOR image has the cast?
    If your inkjet print has a cast, you can probably adjust it out by
    tweaking your printer driver in advanced mode.
    Are you using Generic inks?
    When the cast occurs, does the it occur with all papers?
    The more info you present the more likely you are to get a good answer.
    Bob Williams
    Bob Williams, Oct 23, 2005
  4. Peter

    Peter Guest

    The cast doesn't appear on the monitor because I don't want to see it, but
    with a print and a comparison I can see casts. When I go back to Photoshop
    it's confirmed, my color correction is out. I missed it somehow. As for
    printing I usually correct it somemore with soft proofing. I'm using the
    epson r2400 and everything I use is epson, I've not ventured out with
    different papers and such.

    The problem really lies in my unscientific placement of the gamma sliders in
    levels, I'm just eyeballing it and I feel that a more exact method is
    required here.

    Peter, Oct 23, 2005
  5. Peter

    JFV4492 Guest

    If there are true gray tones in the image, *and* if the gray tones are
    not supposed to have cast, then monitor the Info palette values while
    you color correct. In such areas, a true gray without cast should be
    r=g=b. But true gray areas without any intended cast often do not exist
    in an image. Think white sheet of paper lit but candle light.
    JFV4492, Oct 23, 2005
  6. Peter

    tacit Guest

    Use curves, not Levels, for color correction. Using Curves allows you to
    perform much more precise color correction.
    tacit, Oct 23, 2005
  7. Peter

    Peter Guest

    I've read up on your posts and have done some reading thanks to your
    insight. As for curves, I will have to start using it, I've been putting it
    off long enough, no doubt. However because I started this latest assignment
    in Levels I'll keep it for this one. What I've now opted to use is color
    correction by numbers. I've been picking out my highlight and shadow based
    on the threshold option in the adjustment menu. I use the color picker to
    identify these points. I then put in the readings from the info menu and add
    it in the levels menu. This appears to kill the cast. Now as for highlights?
    In rgb I slide the gamma to lighten my images (grey cloudy day). How do I
    know when enough is enough and when does posterization become a factor. Now
    the reason I ask how much is sufficient consistency is gold.

    Many articles site to pick out neutral areas that are supposed to be or you
    think are grey, I try to avoid guessing. This seems unrealistic to me cause
    on many a day your monitor may be out or light in you computer darkroom may
    affect the visual.....

    Your input is greatly appreciated

    Thank You Peter
    Peter, Oct 23, 2005
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